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| Home > Publications database > Entwicklung von plasmagespritzten Schichten zum Schutz des Faserverbundwerkstoffes C/SiC vor Korrosion bei hohen Temperaturen |
| Home > Publications database > Entwicklung von plasmagespritzten Schichten zum Schutz des Faserverbundwerkstoffes C/SiC vor Korrosion bei hohen Temperaturen |
| Dissertation / PhD Thesis/Book | PreJuSER-50840 |
2005
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/302
Report No.: Juel-4169
Abstract: The material C/SiC (carbon fiber enhanced silicon carbide) shows, besides its outstanding positive properties, an undesirable degradation if exposed to air at high temperatures . Therefore, it is the aim of this work to select and evaluate an environmental barrier coating (EBC) for this material. The chosen EBC is composed of mullite and lanthanum hafnate, both showing excellent high temperature properties. If in contact to hot water vapor as in combustion environments, mullite degenerates and loses its silica content. To protect mullite, a lanthanum hafnate layer is added . Both layers are produced via plasma spraying techniques. Additional to the current powder based plasma spraying, a new technique is applied to produce mullite layers, using a sol containing a silicon and an aluminum source as liquid feedstock. Plasma sprayed mullite coatings show segmentation cracks. Changes in spraying parameters, heat treatment, and filling of the cracks have been investigated in order to eliminate these cracks . To produce crystalline mullite layers, a surface temperature of 800 °C on top of the substrate is needed and can be achieved by disabling the substrate cooling. In case of sol-based plasma spraying, there is evidence that a lower substrate temperature might be sufficient. It was not possible to produce a mullite layer via sol-based plasma spraying, as this leads to a quite low deposition rate and therefore a high process time, causing a degradation of the substrate. Even with optimized spraying parameters, the porosity of the lanthanum hafnate layer could not be decreased sufficiently, there is at least an amount of 9 % porosity assigned to microcracks. Also a double layer containing 149 $\mu$m mullite and 55 $\mu$m lanthanum hafnate was prepared and examined. From these findings it is concluded that an environmental barrier coating system, consisting of a segmentation crack free mullite layer and a lanthanum hafnate layer, is capable of protecting C/SiC at high temperatures.
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